Many persons, particularly children, suffer from accumulation of fluid in the middle ear. In a surgical operation, known as a myringotomy or tympanostomy, an incision is made in the tympanic membrane or eardrum to ventilate the middle ear and/or drain the fluid. This simple incision in the tympanic membrane may provide temporary relief, but incisions of the eardrum normally self-heal within a relatively short time. For ventilation/drainage for longer periods, after myringotomy the surgeon inserts a ventilation tube or “grommet” through the incision, thereby providing a vent which equalises the pressure on either side of the eardrum, and allows fluid to be drained from the middle ear. The eardrum soon heals around the waist of the grommet, which is subsequently expelled from the eardrum usually some months later leaving an intact eardrum.
To insert the ventilation tube into the incision in the tympanic membrane, the ear surgeon grasps the tube with a special grasping forceps, and manoeuvres the tube into position. As the ventilation tube is extremely small, typically less than a few millimetres in diameter, and as the tympanic membrane is so delicate, the surgeon must exercise considerable skill and dexterity in the operation.
The ventilation tube is typically in the form of a short tubular conduit having radial flanges at its opposite ends which locate on opposite sides of the tympanic membrane and assist in keeping the ventilation tube in place. (The eardrum has a natural tendency to dislodge the ventilation tube from the incision as it heals). Various designs have been used or proposed for ventilation tubes in order to facilitate their insertion after a myringotomy and the shape and design of the grommet will influence the length of time they are retained within the drum. Many ventilation tubes have a tab extending from an end flange to enable the ventilation tube to be grasped more easily. Examples of such ventilation tubes can be found in U.S. Pat. Nos. 3,807,409; 3,871,380; 4,174,716; 4,650,488; 4,695,275; 4,764,168; 5,137,523; 5,649,932 and 6,042,574. The tabs of the known ventilation tubes generally extend parallel or perpendicularly to the axis of the tube.
It has been found that insertion of the ventilation tube is facilitated if the leading portion of the tube is inserted into the incision in the tympanic membrane at an angle. Known ventilation tubes which have grasping tabs orientated either parallel or perpendicularly to the longitudinal axis of the tube do not place the tube in the preferred orientation for insertion. The surgeon must therefore manoeuvre the grasping forceps to angle the ventilation tube, increasing the difficulty of the operation.
U.S. Pat. Nos. 5,178,623 and 5,207,685 disclose ventilation tubes having grasping tabs angled obliquely to the axis of the tube. The ventilation tube of U.S. Pat. No. 5,178,623 has a cutting edge at the opposite end of the tube from the grasping tab, diametrically opposite to the tab. In use, the surgeon holds the grasping tab with forceps and presses the ventilation tube against the tympanic membrane, firstly to perforate it with the cutting edge, and then to insert the cutting edge and its associated flange through the incision to seat the ventilation tube in the membrane.
The ventilation tubes of U.S. Pat. No. 5,178,623 may permit the incision and insertion steps to be performed by the same instrumentation, namely the ventilation tube itself, but the provision of a cutting edge on the ventilation tube introduces added risk. The cutting edge must be sharp as it is intended to perform the initial perforation of the eardrum. As a myringotomy knife, the ventilation tube, when grasped with forceps by the surgeon, would not be as stable as a regular myringotomy knife, particularly for very thin and flaccid eardrums and excessively thick eardrums. The cutting edge would therefore appear to be less useful to a surgeon, and possibly more traumatic if the cutting edge inadvertently scratches the skin of the external canal of the ear and/or the drum and medial wall lining of the middle ear, resulting in bleeding and unnecessary injury. Thus, rather than facilitating the insertion of the ventilation tube, the provision of the cutting edge on the tube requires greater skill and dexterity by the ear surgeon.
The ventilation tube of U.S. Pat. No. 5,207,685 also poses the risk of trauma from its sharp cutting edge. Moreover, this ventilation tube must be removed after the incision, released by the forceps, and then re-grasped on a second grasping tab for insertion. The ventilation tube is considered unnecessarily complicated and difficult for surgeons and theatre nurses to use.
A significant disadvantage of the ventilation tubes of U.S. Pat. Nos. 5,178,623 and 5,207,685, as well as the ventilation tubes of the other patents identified above, is that they are designed for use in one orientation only. Thus, when picking up the tiny ventilation tubes, the theatre nurse or surgeon must ensure that the tubes are grasped at the correct end. The tubes may need to be moved around to correctly orientate the tab for grasping by the forceps.
U.S. design Pat. No. D371606 shows an ear ventilation tube which appears to be reversible, but the tabs of the illustrated ventilation tube are small and therefore difficult to grasp. Such small tags, if they are designed to aid insertion are very small and their sides do not meet the outer circumference of the flange tangentially. Thus, if this small tag is able to engage a preformed incision in the tympanic membrane, advancement of the grommet will cause it to be pushed bluntly onto the ends of the preformed incision. The grommet will not slide smoothly to widen the preformed incision resulting possibly in excessive force, a sudden give or tear in the eardrum and the resulting hole possibly being too big to hold the grommet within its space.
Moreover, the tabs are orientated parallel to the longitudinal axis of the tube, and hence the tube is not held at the desired orientation by the grasping forceps. The flanges of the ventilation tube of U.S. design Pat. No. D371606 are also angled obliquely to the axis of the tube, which tends to locate the tube at an angle to the eardrum. Such skewed seating of the tube may facilitate dislodgement of the tube from the eardrum.
It is an object of this invention to provide an improved ventilation tube which is reversible, i.e. it may be used in either of two orientations, safe to use, and configured for easy insertion in a tympanic membrane.